The present invention relates to a method and apparatus for measuring the concentration of two sample gas components in a homogeneous sample gas and more particularly to a method and apparatus for determining the concentration of sample gas constituents each having different spectral absorption bands.
Prior art has disclosed methods and apparatus for determining the concentration of several component gases in a sample gas stream. In general, the prior art requires a separate sample cell for each component gas to be measured whether two component gases are to be measured or one component and a reference is to be measured. The need for a separate sample cell for each constituent gas to be measured results in a bulky, and more expensive apparatus for routine sample measurements. The expense primarily results from the cost of an additional infrared source, a larger power supply, and a second sample cell. As a result of the need for multiple channels, manufacturing cost, both in materials and man hours, as well as maintenance costs increase proportionately. Prior art systems which do not require a separate sample cell for each sample gas component being measured required the use of time sharing electronics. Time sharing techniques necessitate the use of expensive and complex mechanics and electronics to separate the responses due to each gaseous component. One method for determining several components in a homogeneous gas sample is disclosed in copending patent application Ser. No. 13,945, "Method and Apparatus for Negating Measurement Effects of Interferent Gases in Non-Dispersive Infrared Analyzers," filed Feb. 22, 1979, abandoned, assigned to the same assignee as the present application, although the described apparatus requires several detectors and complex electronics.